I'm currently reading Richie Furay's autobiography (I find it very interesting, despite knowing precious little about Mr. Furay or his music). He mentions that both Randy and Timothy B. contributed vocals to his 1979 solo album, "I Still Have Dreams" - he doesn't specify which songs though.
Furay was never close with Randy - he thought he was "a bit off-center" and didn't fit into the Poco family - so perhaps his involvement was a suggestion of producer Val Garay, who went on to produce Randy's 1980 album, One More Song. Randy later said Garay had been wanting to work with him "for a few years."
One thing that Furay states (more than once) in his book is that Randy's bass tracks and backing vocals were erased from the first Poco album after he abruptly quit the group. I had previously read elsewhere that while Randy's vocals were erased, they kept his bass tracks. If anyone knows for sure, feel free to weigh in!